Method and apparatus for amplifying frequency currents



y 1934- J. M. AVERY 1,957,752 Y mam'on AND APPARATUS FORIAMPLIFYINGFREQUENCY cunnsuws Filed Aug. -11, 1925 l l-r l l' lmm INVENTOR. Jo/v/vflI/EFK 1 ATTORNEY Patented May 8, 1934.

OFFICE METHQD AND APPARATUS FOR AMPIJFY- ZING FREQUENCY CURRENTS John M.Avery, Flushing, N. FL, assignor, by mesne assignments, to RadioCorporation of America, a corporation of Delaware Application August in,1925, Serial No. c9522 it claims. (oi. ire-r11) This invention relatesto the amplification of pulsating currents, particularly currents of lowor audio frequencies such as are employed for example in telegraph andtelephone systems.

in the amplification of alternating or pulsating currents, particularlyat thelower frequencies, difficulty has been experienced in amplifyingthese currents without modification of their character. This dificultyhas been particularly pronounced, for example, in the amplification ofto certain inherent characteristics of such devices, and heretofore nosatisfactory way of overcoming these difficulties has been devised.

An object of the invention is to provide an improved method andapparatus for amplifying pulsating currents, particularly by iron coretransformers, with which amplification of the currents of allfrequencies may be obtained without distortion or other undesiredvariations therein; and with which variations may be made in the character and range of the amplification.

A further object is to provide an improved ap-' aratus for amplifyingpulsating currents which will accomplish each and all of the objectsabove set forth, and which will be relatively simple, easilymanipulated, and inexpensive.

Various other objects and advantages will be apparent from the followingdescription of one embodiment of the invention, and the novel featureswill be particularly pointed out hereinafter in connection with theappended claims.

in the accompanying drawing, 1 have illustrated a circuit arrangementembodying the invention and employing three cascade coupled vacuum tuberelays.

In the accompanying drawing, the diagram represents the detector andamplifying circuits of a well known type of radio telephone andtelegraph receiving set. In such a set the detector tube 1 is coupled byan iron core transformer 2- to an audio frequency amplifying vacuum tube3 in the usual manner, and the tube 3 is in turn coupled by an iron coretransformer 4 to a second audio frequency amplifying tube 5 in the usualmanner. The filament electrodes 6 of the tubes are supplied with currentby circuit wires 7 connected 'to a suitable source of energy A in theusual manner. High frequency currents, either directly from an antennacrcuit or from a radio frequency amplifying system, are impressed uponthe input circuit 8 of the detector tube 1 in the usual manner.

The plate circuits of .the various tubes are supplied with current orpotential from a suitable source, such as a battery B. For example wires9, 10 and 11 connect the battery or other source of B potential with theprimary windings of the transformers 2 and 4 and with the output circuitrespectively. The primary windings of the transformers, and the otherside of the output circult of the last tube, are connected by wires. 12,13 and 14 with the platesv of their respective tubes, as usual incascade couplings. The circuits just described may be the usual circuitsemployed for the cascade coupling of the tubes utilizing iron coretransformers between successive tubes.

A variable resistance 15 is connected at one endby a wire 16 to theplate of the'detector tube 1, and at its other end by a wire 1'7 to oneside of a suitable condenser 18, the other side of r the latter beingconnected by a wire 19 to the grid electrode of the next successivevacuum tube 3. The condenser and variable resistance 15 are thusconnected in series with one another and in shunt across the iron coretransformer 2. A similar coupling correspondingly indicated but with theexponent a added to the reference characters is provided between theaudio frequency'amplifyingtubes 3 and 5 and across the transformerPreferably, although not essentially, the variable resistances 15 and15a are connected for simultaneous operation by a single control,although such connection may be such as to permit of the independentadjustment of such resistances relatively to one another.

Without the by-pass circuits across the transformers 2 and 4, the systemillustrated would amplify audio frequency currents of certainfrequencies or of certain frequency bands with great efficiency shouldthe condition exist that the impressed frequencies were ldentical withthose for which the transformer-was most efficient, but for otherfrequencies outside these values a. lesser, distorted, and objectionableamplification would be given. By shunting, however, a portion of theaudio frequency currents directly between the successivelycoupled' tubesand across the transformers'connecting them, those currents which arenot efiiciently amplified by the transformers will be transferredbetween the tubes with some amplification and without amplification ordistortion caused by the transformers.

1 sets, it has been found that tone values produced from this audiofrequency amplifying system,

are dependent upon the values of the resistors 15 and 15a and thecondensers 18 and 18a, and that the tones may be varied at will byvariations of these elements in order that they might more readilyby-pass currents of varying frequencies and frequency bands.

Inasmuch as one usually desires" to properly amplify given frequenciesof currents, it is of advantage to couple the variable elements of theby-passcircuits for simultaneous operation by a single control asindicated on the drawing, but obviously they could be separatelymanipulated and adjusted, if desired. The coupling between the variableparts of the variable elements of the by-pass circuits permits ofrelative adjustment of the different variable elements in order that forany indication of the common operating membenthe efiect will be uniformin all by-pass circuits. By varying the adjustable elements of theby-pass circuits, separately or together, the character of theamplification may be varied and in radio telephone systems, the tonevalues amplified may be varied. B

The variable resistance 15 and condenser 1'7 constitute a variableimpedance unit, and while other variable impedance units may beemployed, I have found that this particular unit is very satisfactory.The variation of the impedance is easily and satisfactorily obtained byvariation of the resistance, but obviously the condenser may also orinstead be varied in order to vary the impedance.

- the primary and secondary windings of each transformer for variablyshunting a portion of the audio currents around the coupling betweensuccessive relays whereby'said shunted currents are transferred withoutdistortion.

2. An audio frequency amplifier comprising a plurality of thermionicrelays, means including iron core transformers for coupling said relayssuccessively, a by-pass circuit connected directly between the "anodeand control electrode of successive relays and around the primary andsecondary windings of each transformer for variably shunting a portionof the audio currents around the coupling between successive relays 3.An audio frequency amplifier comprising a plurality of vacuum tuberelays, an iron core transformer coupling said relays to permit of thetransfer and amplification of the audio currents between the same, and aby-pass circuit between the plate of one relay and the grid of the nextsuccessive relay, including therein a condenser and resistance, forshunting a portion of said current directly between said relays withoutdistortion of the shunted current.

4. A frequency current amplifier comprising a plurality of vacuum tuberelays, an iron core transformer coupling said relays to permit of thetransfer and amplification of the currents between the same, and aby-pass circuit between the plate of one relay and the grid of the nextsuccessive relay, including therein a condenser and a variableresistance connected in series with one another and in said circuit, forshunting a portion of said current directly between said relays withoutdistortion of the shunted current.

5. An audio frequency amplifier comprising a plurality of thermionicrelays, iron core transformers for coupling said relays successively topermit of the transfer of audio frequency energy between the same, and aby-pass circuit connected directly between the anode and controlelectrodeof successive, relays, each circuit including therein animpedance between said relays for by-passing around the coupling betweenrelays those audio frequencies which are ineffectively handled by thecoupling means.

6. In an audio frequency amplifier, employing a plurality of vacuumtubes in cascade arrangement, coupled by transformers, a condenser inseries with a resistance, connected between plate terminal of any vacuumtube and grid terminal of succeeding tube.

7. In an audio frequency amplifier system. including at least twoelectron discharge tubes connected in cascade by transformer coupling, apath including a condenser and resistor connected between the anode ofone of the tubes and the control electrode of the succeeding tube, saidresistor being adjustable for varying at will the tone value from theamplifier.

8. In an audio frequency amplifier employing vacuum tubes in cascade, acoupling arrangement between tubes comprising, in combination,transformer coupling means and resistance-condenser coupling meansassociated therewith, and means for bringing into predominant actioneither of the aforesaid coupling means. I

9. In an audio frequency amplifier employing vacuum tubes in cascade, acoupling arrangement between tubes comprising, in combination,transformer coupling means and resistance-condenser coupling meansassociated therewith, and means for adjusting the relative amounts ofpower to be passed by each.

10. In a system for amplifying currents of the audio frequency range, atleast one amplifier tube,

a source of said currents, the input electrodes of said tube beingconnected to said source, a load adapted to utilize the amplifiedcurrent output .of said tube, an audio frequency coupling networkconnecting the said load to the output electrodes of said tube, and anaudio frequency b'y-pass path, including a resistor and condenser inseries,

the relative magnitudes of said resistor and condenser being so chosenthat the tone value produced from the system depends on the frequency ofcurrents by-passed by said path, said resistor being adjustable to varyat will the said tone value.

11. In a system for amplifying currents of the audio frequency range, atleast one amplifier tube, a source of said currents, the inputelectrodes of said tube being connected to said source, a load adaptedto utilize the amplified current output of said tube, an audio frequencycoupling network connecting the said load to the output electrodes ofsaid tube, and an audio frequency by-pass path, including a resistiveimpedance and a condensive'impedance in series, electrically associatedwith said coupling network, the relative magnitudes of said resistor andcondenser being so chosen that the tone value produced from the systemdepends on the frequency of currents by-passed by said path, at leastone of said impedances being adjustable to vary at will the said tonevalue.

12. In a radio telephone receiver, a detector of audio modulated radiofrequency currents, an audio frequency amplifier for amplifying thedetected currents, said amplifier including at least one amplifier tubehaving its input electrodes connected to the detector output circuit, anaudio frequency network, coupled to the output electrodes of said tube,for transmitting amplified audio frequency currents to the reproducer ofsaid receiver, an aperiodic tone control impedance path electricallycoupled to said network, said path including a resistor and condenser inseries, and the relative magnitudes of said resistor and condenser beingso chosen that the tone value of the reproduced amplified audiofrequency currents depends on the audio frequencies shunted through saidtone control path.

. 13. In a radio telephone receiver, a detector of audio modulated radiofrequency currents, an

audio frequency amplifier for amplifying the detected currents, saidamplifier including at least one amplifier tube having its inputelectrodesconnected to the detector output circuit, an audio frequencynetwork, coupled-to the output electrodes of said tube, for transmittingamplified audio frequency currents to the reproducer of said receiver,an aperiodic tone control impedance path connected to the anode of saidtube and being electrically coupled to said net work,-

said path including a resistor and condenser in series, and the relativemagnitudes of said resistor and condenser being so chosen that the tonevalue of the reproduced amplified audio frequency currents depends onthe audio frequencies shunted through said tone control path.

14. In a radio telephone receiver, a detector of audio modulated radiofrequency currents, an audio frequency amplifier for amplifying thedetected currents, said amplifier including at least one amplifier tubehaving its input electrodes connected to the detector output circuit anaudio frequency network, coupled to the output electrodes of said tube,for transmitting amplified audio frequency currents to the reproducer ofsaid receiver, an aperiodic tone control impedance path connected totheanode of said tube and being electrically coupled to said network,said path including a resistor and condenser in series, and the relativemagnitudes of said resistor and condenser being so chosen that the tonevalue of the reproduced amplified audio frequency currents depends onthe audio frequencies shunted through said tone control path and asecond tone control path, including a resistor and condenser, connectedto the input circuit of said amplifier tube.

15; In a radio telephone receiver, a detector of audio modulated radiofrequency currents, an audio frequency amplifier for amplifying thedetected currents, said amplifier including at least one amplifier tubehaving its input electrodes connected to the detector output circuit, anaudio frequency network, coupled to the output electrodes of said tube,for transmitting amplified audio frequency currents to the reproducer ofsaid receiver, an aperiodic tone control impedance path electricallycoupled to said network, said path including a resistor and condenser inseries, and the relative magnitudes of said resistor and condenser beingso chosen that the tone value of the reproduced amplified audiofrequency currents depends on the' audio frequencies shunted throughsaid tone control path and an aperiodic tone control path, including aresistor and condenser, connected to the input circuit of said amplifiertube, and means for simultaneously adjusting the magnitudes of theresistors of both said paths.

16. In a radio telephone receiver of the type comprising a detector anda succeeding audio amplifier, the amplifier including a pair of cascadedtubes, and the last tube being adapted for connection to the receiverreproducer, a tone control device for varying at will the tone values ofthe reproduced amplified audio frequency currents, said deviceconsisting solely of a resistor and condenser in series with each other,the device being electrically connected between the detector outputcircuit and-the input circuit of the first of said cascaded tubes, therelative values of said resistor and condenser being such that audiocurrents of varying frequencies may be by-passed through said device.

1'7. In a radio telephone receiver of the type including an audiofrequency amplifier provided with at least one amplifier tube, acoupling means between the input circuit of said tube and the receivercircuit preceding said input circuit, the output terminals of saidcoupling means having a substantially higher impedance at high audiofrequencies than at low audio frequencies, and an aperiodic tone controlpath shunted across said coupling means, said path including a resistorelement and an element whose impedance value varies with appliedfrequencies, and means for adjusting the impedance value of one of saidpath elements to thereby vary the effective impedance across saidterminals.

JOHN M. AVERY.

